1. Field of the Invention
This invention relates to means for controlling a microwave circuit and more particularly to an optically controlled MESFET using an interdigited photoconductive detector for controlling microwave circuit functions by optical means.
2. Description of the Prior art
Conventional distribution networks such as coaxial transmission lines and metallic waveguides are bulky and susceptible to radiation environments. Optical wave guides such as fiber optics have become a viable means for the distribution of microwave signals and control signals. This is principally due to two causes, first the low cost of optical fibers, and secondly, the increased operational speed of lasers and photodetectors. Distributing the various control signals by optical fibers has many desirable features such as high speed, large bandwidth, good electrical isolation and elimination of grounding problems. Also, optical fibers are relatively light in weight and can be configured in relatively small sizes.
Optically controlling microwave circuit functions such as gain, phase or switching requires detection and amplification of optical signals. Additionally, optical detectors must be compatible with gallium arsenide (GaAs) microwave monolithic integrated circuit (MMIC) fabrication techniques to provide monolithic integration of optical and microwave components. Known prior art apparatus used GaAs MESFETs as an optical detector with additional amplification stages to provide control of gain, phase and switching of microwave circuits. Such apparatus is shown and described, for example, in U.S. Pat. No. 4,859,965, entitled, "Optical Gain Control Of GaAs Microwave Monolithic Integrated Circuit Distributed Amplifier", issued to Arthur Paolella et al on Aug. 22, 1989.